The microstructural and microchemical evolution of Fe-15Cr-XNi and ISCr-85Ni austenitic alloys irradiated with fast neutrons at 510 and 538°C and heavy ions at 675°C was investigated to determine whether common mechanisms of nickel's influence on microstructural development existed under different irradiation conditions. A surprising commonality for these two types of irradiations was observed involving nickel-dependent void densities, dislocation and loop dominance of dislocation structures, and fluence dependence of swelling, void density, and solute segregation. Quantitative analyses of microstructure and microchemistry data snowed that the variation of dislocation sink strength with nickel addition may provide the major mechanisms by which swelling depends on nickel content. Other processes, such as nickel's influence on the mobility of vacancies and the different segregation behavior at sessile and mobile defects, also cooperate to produce the overall behavior.

The objectives of this effort is to identify the mechanisms involved in the radiation-induced evolution of microstructure in materials intended for fusion applications. The results of this study are useful in interpreting the results of several other ongoing experiments involving either spectral or isotopic tailoring to study the effects of helium on microstructure evolution. Ion-irradiated Fe-15Cr-XNi (X = 20, 35, 45, 60, 75) ternary alloys and a 15Cr-85Ni binary alloy were examined after bombardment at 675°C and compared to earlier observations made on these same alloys after irradiation in EBR-II at 510 or 538°C. The response of the ion-irradiated microstructures to nickel content appears to be very consistent with that of neutron irradiation even though there are four orders of magnitude difference in displacement rate and over 200°C difference in temperature. It appears that the transition to higher rates of swelling during both types of irradiation is related to the operation of some mechanisms that is not directly associated with void nucleation. 6 refs., 8 figs.

Symposium held in Nashville, Tennessee, June 1990. Almost two-thirds of these 91 papers are authored by researchers outside of the US (including information on research in the former USSR, Japan, and Europe). Topics include: current commercial power reactor systems; microstructural characterization

Fe-16Cr-17Ni ternary alloy and those with addition of 0.024P, 0.1P and 0.1P+0.25Ti were irradiated with fast neutrons in FFTF/MOTA at 793 K and 874 K to 33 dpa and 60 dpa. For the purpose of investigating helium production effect, two levels of 10B were doped for each alloy. The microstructures and their relation with tensile properties were examined. The yield stress change was correlated with the density of phosphide precipitates.